In recent years, research and development of satellite communication technology using antenna apparatus have been under way. In order to achieve high-speed communications, it is necessary to use an antenna apparatus with high gain and low interference.
To achieve high gain, antenna apparatuses of a system in which a service area is covered with a plurality of spot beams have been studied. In the system of covering a service area with a plurality of spot beams, it is possible to achieve higher gain than in the case of a general contoured beam antenna.
As to interference, which is generally evaluated by carrier-to-interference ratio (C/I), adjacent beams typically use different frequencies or polarizations to achieve low interference. That is, multiple combinations of frequency and polarization are prepared such that adjacent beams do not use the same combination of frequency and polarization.
As a result, interference between adjacent beams can be suppressed. However, interference may occur between beams using the same combination of frequency and polarization.
In an antenna apparatus disclosed in the following Patent Literature 1, interference waves are reduced by using multiple antenna elements to form one beam and using different excitation coefficients for the multiple antenna elements.